This invention claims priority from Korean Patent Application No. 2001-5339, filed Feb. 5, 2001, the contents of which are herein incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a system and method for detecting a position of a semiconductor wafer and more particularly, to a system and method that determines whether the wafer is normally positioned before executing a process, to prevent process defects.
2. Discussion of Related Art
In facilities for fabricating semiconductor devices, a vacuum pressure environment is generally used to prevent pollution and maintain the purity of a wafer. Bake oven facilities, for example, typically use vacuum pressure conditions. In a bake oven, an outer housing is generally made of opaque material, such as metal, to provide durability and airtightness. Because of this, however, it is difficult to determine whether a wafer is properly positioned within the bake oven and whether the process was properly executed.
To perform a process, the wafer is first positioned on a chuck plate. A conventional procedure for placing the wafer on the chuck plate, and its attendant difficulties, will be described with reference to FIGS. 1 and 2. Referring to FIG. 1, a general robot unit (not shown) places a wafer W in position on an upper part of a chuck plate 10 inside a fabrication unit, such as a bake oven. The chuck plate 10 includes elevator pins 12 which move vertically up and down. As the wafer is placed in the fabrication unit, the elevator pins 12 are elevated to prop up and support a lower face of the wafer W. After the robot unit places the wafer W it is withdrawn. When the robot unit is retracted from the wafer W, the elevator pins 12 are lowered to bring the lower face of the wafer W to rest on the upper face of the chuck plate 10. The wafer W can be positioned and maintained on the upper face of the chuck plate 10 using special equipment, or the wafer W may be positioned and fixed using a general fixing unit (not shown) installed on the chuck plate 10. Once positioned, the wafer W receives a desired environmental condition (such as a temperature state, an electric characteristic, etc.) through a condition forming part 14 installed on the chuck plate 10.
Unfortunately, a wafer particle or other particle P may unseat a lower face of the wafer W from an upper face of the chuck plate 10. If the wafer W rests unevenly on the chuck plate 10, the environmental condition provided by the condition forming part 14 will not be properly applied to the wafer, thus resulting in a process defect.
Referring to FIG. 2, besides process defects resulting from particles unseating the wafer W from the chuck plate 10, defects may also result from poor alignment of the wafer W on the chuck plate 10. A procedure for positioning the wafer W on the chuck plate includes a series of steps. The robot unit conveys the wafer W to the chuck plate 10. The wafer W is then transferred from the robot unit to the elevated elevator pins 12. The elevator pins are then lowered to place the wafer in contact with the upper face of the chuck plate 10. During these steps, however, various kinds of shocks, vibrations, or the like may cause the wafer W to be placed off-center from a proper position on the chuck plate 10. If such an operation error occurs, a portion of the wafer may hang over an edge of the chuck plate 10. If the wafer W is improperly positioned in this manner, the process will be performed non-uniformly over the face of the wafer W. Furthermore, if the wafer W overlaps a previously positioned wafer on the chuck plate 10, not only will a pattern layer formed on the wafer W be damaged, but the next procedure will also be adversely affected.
A conventional solution to these problems is to form a transparent window in the fabrication unit to allow a user to see into a given portion of the unit. A window, however, does not readily permit a determination that the wafer W is unseated when its separation from the chuck plate 10 is minimal. Furthermore, the window only permits viewing of the wafer W from a specific, fixed position. It would be desirable in the industry to have a system and method for detecting semiconductor wafer position that would automatically correct certain defects in wafer positioning. It would also be desirable to have a system and method for detecting semiconductor wafer position that would permit detection of even minute displacements of the wafer from the chuck plate surface.
Accordingly, the present invention is directed to a system and method for detecting a position of a semiconductor wafer that substantially obviates one or more of the limitations and disadvantages of the related art.
A primary object of the present invention is to provide a system and method for detecting a position of a semiconductor wafer, in which process defects and wafer damage can be prevented to increase fabrication yield. The system and method preferably provide easy verification of wafer position to permit determination of whether the wafer has been properly transferred to a chuck plate, whether the wafer has been placed in the right position on the chuck plate, whether the wafer is folded, and whether the wafer is separated from the chuck plate.
In accordance with a preferred embodiment of the present invention, a system for detecting a position of a semiconductor wafer includes a chuck plate having a supporting part, for supporting a lower face of a wafer, and a guide part formed on an outer perimeter of the supporting part. A sensing unit senses a position of the wafer on an upper portion of the supporting part and transmits a sensing signal to a controller. The controller preferably receives the sensing signal, corresponding to the wafer position, from the sensing unit, and transmits an output control signal to an outputting unit based on the sensing signal. The outputting unit can include a bell unit for outputting alarm sound, a lamp unit for outputting light, a monitoring unit for supplying a video image, and/or a switching unit for selectively cutting off power applied for respective constructions of the fabrication facilities.
An upper side portion of an inner side wall of the guide part is preferably provided with an inwardly slanted face so as to direct a wafer positioned on the guide part toward a center of the chuck plate. The supporting part and the guide part can be formed integrally or assembled together in an operating relationship. If assembled from separate components, the guide part could be constructed to move up and down in relation to the supporting part in response to a driving control signal from the controller. It may also be desirable for the guide part to be provided in at least two segments arranged at given intervals along an outer perimeter of the supporting part. A lower part of the chuck plate can include a rotating unit configured to rotate the supporting part in response to a rotation control signal from the controller.
The sensing unit is preferably constructed having optical sensors. The optical sensors can be configured to supply irradiating probe light against an edge portion of the wafer positioned on the supporting part and to receive and sense an amount of light reflected or diffracted therefrom. In one configuration, the optical sensors can be installed between the guide part segments. Alternatively, the optical sensors can be installed in opposing pairs along the inner wall of the guide part, with each sensor in a pair being located on an opposite side of a center of the supporting part. A plurality of light emitting and receiving sensors could also be disposed in various vertical positions along the guide part inner wall.
A method of detecting a position of a semiconductor wafer is also provided. The method includes supporting an edge portion of the wafer on a guide part and placing the wafer on a supporting part. A position of the wafer on the supporting part is sensed using a sensing unit during a sensing operation. A measurement value obtained through the sensing operation is then compared with a determination value range to detect and output an adhesion state and a positional state of the wafer.
To sense the positional state of the wafer on the supporting part, the sensing unit can be constructed having light emitting and receiving sensors arranged in pairs opposite each other across the supporting part. A plurality of light emitting and receiving sensors can be disposed in various elevations along the guide part inner wall so as to sense the positional state of the wafer along an upper face of the supporting part. Alternatively, the light emitting and receiving sensors can be arranged in opposing pairs at a single elevation with the guide part configured to be raised or lowered in relation to the supporting part. In this configuration, the sensors can sense the positional state of the wafer on the upper face of the supporting part as the guide part elevates and descends.
Sensing the positional state of the wafer on the supporting part could also be accomplished by constructing the guide part with at least two segments arranged at given intervals along an outer perimeter of the supporting part. In this embodiment, the supporting part is configured to selectively rotate. The sensing unit includes an optical sensor that transmits probe light between the segments of the guide part against an edge of a wafer positioned on the rotatable supporting part. As the supporting part is rotated, the optical sensor senses an amount of light reflected or diffracted from the wafer to determine the positional state of the wafer on the upper face of the supporting part.